An optical coupling device, which is one example of an optical semiconductor device, has a structure in which an optical element serving as a light emitter or a light receiver is disposed on a lead frame and the optical element is covered with a light transmitting member, such as a resin. In a case where the optical coupling device is used in a strict environment under high temperature and high humidity there are concerns that characteristics of the optical coupling device may be affected due to peeling and thermal deterioration of the resin.